The present disclosure relates to compensating for a charge in a silicon substrate. In particular, the present disclosure relates to forming a harmonic suppression layer at a boundary of a buried oxide (BOX) layer and a silicon substrate.
A silicon wafer for forming semiconductor devices may be formed by providing a silicon substrate and doping a layer of the silicon substrate with oxygen to form a buried oxide (BOX) layer between a thin active silicon layer and a handle substrate layer. The handle substrate layer may be manufactured to have a high resistivity, such as by doping the handle substrate layer. When oxygen is introduced into the handle substrate layer in the crystal manufacturing process, the oxygen may result in undesirable effects in semiconductor circuitry formed in the thin active silicon layer. In particular, when oxygen in the handle substrate near the border of the BOX layer is annealed, as during the semiconductor manufacturing process, the oxygen may generate donor complexes that provide free electrons, resulting in the generation of harmonics when semiconductor circuitry in the thin active silicon layer operates at a radio frequency (RF).
Harmonic generation is minimized when free carriers are minimized in the handle substrate layer near the BOX layer. The carrier concentration near the surface of the handle substrate depends on the charge at the oxide interface, substrate resistivity and carrier type, and interstitial oxygen concentration together with annealing history.
Generally, manufacturers of silicon wafers provide guarantees that resistivity of the substrate doping falls within certain bounds, and that oxygen in the handle substrate will be less than a predetermined amount. In addition, effort is made to minimize variation in oxide interface charge. However, these parameters will vary between manufacturers and between batches supplied from the same manufacturer. For example, interstitial oxygen may be specified as less than ten (10) parts per million atoms (ppma). Even so, small amounts of oxygen in the handle substrate, such as around four (4) ppma or greater may adversely affect performance of semiconductor circuitry, depending on a resistivity of the handle substrate.